﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo0506
{
	class Program
	{
		static void Main(string[] args)
		{
			Console.WriteLine("Hello World!!");
			Console.WriteLine("请输入圆的半径：");
			double R =double.Parse( Console.ReadLine());
			double circle = R * R * 3.14;
			Console.WriteLine("圆的面积是：" + circle);
			Console.ReadLine();
		}
	}
}
